In Mosaic app, when I switch the input in audio tap and then play Qubuz after choosing rossini icon, the Mosaic cannot connect soon. So, I have to close Masic app and open it again.
Is it normal? Or is there any other way I can switch the input and play Qobuz without reopen Mosaic app?
Yes, if I understand you correctly this should not happen and is probably the result of Mosaic having issues with discovering or maintaining contact with your dCS unit ( and via that Qobuz).
This kind of thing is not uncommon but virtually always is caused by some problem with your network. The most usual concern is one of its settings ( i.e. in your switch or router software). It’s comparatively easy to fix.
You may want to get advice from a man that knows and that isn’t me 
. Contact support at dCS:
Thank you for the commenta.
I will send the questions to dCS for their advice 